Quite a few reports coming in from folks who are finding Palmer Amaranth up in their fields. We have found some that were over an inch tall today (March 20). Some have expressed concern that the Palmer amaranth is up this early. Though it definitely could be an issue if allowed to get large and thick by planting, it could also be a positive. One of the best ways to deplete the soil seed bank of Palmer is though germination and then controlling the young seedlings. Controlling this early emerged Palmer can be accomplished easily with tillage, paraquat, dicamba, 2,4-D or Verdict if it is small. However if it gets up over 12” tall and thick by planting time then tillage can be very inconsistent controlling Palmer amaranth. Moreover, herbicide applications can also result in spotty control due to coverage issues on thick pigweed stands.
There was quite a bit of Leadoff used for residual control back in early March. These fields should stay clean for winter annuals but will likely have some Palmer break. I would not expect a total Palmer jail break as the Leadoff will provide some residual control. However, it will not provide the residual of Valor or even Verdict on Palmer come April 1. Regardless of the residual used in the early March burndowns, by the first week of April, with the weather we have had, expect the Palmer to break in all of them. As I mentioned in the March 13th blog we have moved to a two Burndown system in order to manage GR horseweed and GR Palmer amaranth. With the early Palmer emergence we may have to do a third burndown trip in some fields. This is particularly true if the pigweed becomes very large and thick by the time we can get it sprayed. These fields may need a sequential application of a paraquat product spaced about 7 days apart to provide complete Palmer control. One of those applications should have a PSII inhibiting herbicide (atrazine, simazine, Cotoran, Caparol, metribuzin, etc.) tankmixed in with it to help provide control.
Dr. Larry,
How much of our Palmer is ALS resistant also? And if it is, would our ALS chemistries like Leadoff provide residual control in that situation?
thanks
Greg and Tom
Thanks for the comments. Anywhere from 60 to 80% of our Palmer is ALS resistant. However, as Tom said we get some help from ALS herbicides on Palmer pre where we do not see that post. A good example is comparisons we have done comparing valor xlt compared to valor. We see more consistent control with the xlt product.
I think it is a case that the resistance is still there. Small seedlings are just more susceptible even with some tolerance. If you think about the LD 50 concept i.e. Mg of herbicide to kg of body weight, there is very little body weight with a small germinating seedling. The same thing is going on up in Illinois with the ppo resistant waterhemp. Pre they get some control and post they do not. Along these lines your comment last week of tank mixing Leadoff with Sharpen makes a lot of since on springs like this when the Leadoff could use a little help from Sharpen on early emerging pigweed.
Larry
Greg,
In our research we have seen a benefit from ALS-inhibiting herbicides applied PRE even with known ALS-resistance. ALS herbicides are not enough as a stand alone system but when applied with other residuals they do bring something additional to the table. University of Georgia has reported similar results as well.
Tom
Tom
You are likely seeing more Palmer up in Mississippi than we are. Have you changed your burndown recommendation?
Thanks
Larry
Thanks guys! Like you said initially, Larry, this is going to be a 2 to 3 burndown year especially with all this rain. We got the warm weather, but we seem to be going out earlier and earlier with burndowns and eventually they are going to play out. Early burndowns are great to help manage acres, however, if crops don’t also get in the ground earlier in years like this extra applications are inevitable. With this year, I guess all bets are off and obviously with significant amounts of Palmer breaking mid-March with other summer annuals probably not too far behind, the “Start Clean, Stay Clean” message is sure to be tested. I’ve had a couple of questions this week on what size Pigweed Verdict/Sharpen will control? For those that haven’t seen what Verdict can do POST to pigweed check it out…residual isn’t to shabby either.
Next weed question…Is good old marestail done germinating at this point. Back in the day (really just 10 to 12 yrs ago) when all the resitance hit west TN. Wasn’t the thought from the original biology studies that the primary flush (understanding that marestail can emerge from September thru June) of marestail emergence (approx 80%) occurs late March through 1st part of April. I realize that’s a +/- deal depending on the year, but do we expect to see a big flush of horseweed yet to come?
thanks again
-g
Greg
Yes, we can expect another flush of horseweed yet this spring. The fall emerging horseweed is typical the harder to control as it is well established by now.
Larry